Application - Hitachi Relion 670 Series Applications Manual

1MRK511407-UUS Rev. N
10.4.2

Application

Generator prime movers are affected by abnormal frequency disturbances. Significant frequency
deviations from rated frequency occur in case of major disturbances in the system. A rise of frequency
occurs in case of generation surplus, while a lack of generation results in a drop of frequency.
The turbine blade is designed with its natural frequency adequately far from the rated speed or multiples
of the rated speed of the turbine. This design avoids the mechanical resonant condition, which can lead
to an increased mechanical stress on turbine blade. If the ratio between the turbine resonant frequencies
to the system operating frequency is nearly equal to 1, mechanical stress on the blades is approximately
300 times the nonresonant operating condition stress values. The stress magnification factor is shown in
the typical resonance curve in Figure 75.
300
250
200
150
100
50
IEC12000611 V2 EN-US
Figure 75:
Each turbine manufactured for different design of blades has various time restriction limits for various
frequency bands. The time limits depend on the natural frequencies of the blades inside the turbine,
corrosion and erosion of the blade edges and additional loss of blade lifetime during the abnormal
operating conditions.
The frequency limitations and their time restrictions for different types of turbines are similar in many
aspects with steam turbine limitations. Certain differences in design and applications may result in
different protective requirements. Therefore, for different type of turbine systems, different
recommendations on the time restriction limits are specified by the manufacturer.
Phasor measurement unit RES670
Application manual
-
1.0
Frequency or Resonant Frequency
Ratio
Typical stress magnification factor curve according ANSI/IEEE C37.106-2003
Standard
© 2017 - 2023 Hitachi Energy. All rights reserved
+
IEC12000611-2-en.vsd
Section 10
Frequency protection
GUID-82CA8336-82BE-42AB-968A-D4F08941C9D0 v3
165